Why is this an issue?

Sharing some naming conventions is a key point to make it possible for a team to efficiently collaborate. This rule allows to check that field names match a provided regular expression.

Noncompliant code example

With the default regular expression ^[_a-z][_a-z0-9]*$:

class MyClass:
  myField = 1

Compliant solution

class MyClass:
  my_field = 1